The present invention relates to an extendable column and more particularly to an extendable column utilizing screws to extend and retract a plurality of axially elongated sections which telescope within each other.
In the design of a large deployable parabolic antenna for space application a need arose for an extendable column capable of extending up to ten times its initial length. This capability is necessary to enable the antenna to be collapsed for transport aboard the space shuttle.
A variety of extension designs were investigated, including systems using cables, hydraulics and airjacks, but proved inadequate. In space application the use of hydraulic or airjack systems is precluded by the risk of leaks and subsequent system failure. Cable systems are complex and prone to failure especially in a weightless environment where opposing sets of cables are required.
The present invention utilizes screws to extend sections which telescope within each other. Each section includes a set of screws interconnected by a chain and sprockets to enable simultaneous rotation thereof. Rotation of the screws in one section results in telescoping the next inner section having threaded bosses engaging the screws. The section screws are driven by a common motor being selectively engaged therewith by clutch mechanisms to extend the column to the desired length.
The use of screws to interface the extended section provides excellent structural integrity, low compliant joints, and zero backlash since once extended, the sections are bolted tightly together. Also, the column is capable of supporting both compressive and tensile loads during extension and retraction affording a high degree of safety in operation under loaded conditions.
An object of the present invention is an extendable column capable of extending up to ten times its original length.
A further object of the invention is an extendable column with low compliant joints and zero backlash.
A further object of the invention is an extendable column capable of supporting loads during extension and contraction.
A further object of the invention is an extendable column having a plurality of structural sections which telescope within each other having screws threadingly engaging an adjacent section to extend or retract the column by rotation of the screws.
Another object of the invention is an extendable column which yields the foregoing advantages and which utilizes a single motor and a plurality of clutches to selectively extend or retract the structural sections of the columns.
Another object of the invention is an extendable column which yields the foregoing advantages and which utilizes chains and sprockets to drivingly connect the motor with the clutches.
Other objects and advantages of the present invention will be readily apparent from the following description and drawings which illustrate preferred embodiments of the present invention.